There are many types of topical antiperspirant products that are commercially available or otherwise known in the antiperspirant art. These products typically contain an antiperspirant active in the form of an aluminum and/or zirconium salt, and the majority of these products contain a combination of aluminum and zirconium salts as the antiperspirant active.
These combinations of aluminum and zirconium salts for use as antiperspirant active comprise aluminum and zirconium hydrolysis polymers formed by the partial neutralization of acidic aluminum (Al+3) and zirconium (Zr+4) metal ions. These active materials are most typically made by mixing basic zirconium salts (e.g., zirconium hydroxy chloride) and basic aluminum salts (e.g., aluminum chlorohydrate) in an aqueous solution and then spraying dry the aqueous solution to produce a solid zirconium-aluminum salt. This type of process generally requires the use of a buffer such as glycine to prevent precipitation of the salts during the aqueous mixing process.
Recent methods for making zirconium-aluminum salts have been directed to the formation of those zirconium-aluminum salts having enhanced antiperspirant activity. Such methods typically involve heating a solution of an aluminum salt and a zirconium salt to allow the salts to react while in solution to form a new zirconium-aluminum salt comprising smaller and more effective aluminum hydrolysis polymers. When the desired polymer size distribution is achieved during the mixing and heating process, the heated mixture is typically spray dried to form a solid zirconium-aluminum salt having improved antiperspirant activity.
There are many different methods described in the art for making zirconium-aluminum salts. The antiperspirant art teaches that most or all of these methods must involve at least one process step in which aluminum salts and zirconium salts are mixed together in an aqueous solution to allow the two salts to react and form a zirconium-aluminum salt comprising an aluminum polymer distribution suitable for use as an antiperspirant active.
An example of one such method is described in U.S. Pat. No. 5,589,196 (Callaghan et al.) which teaches a process in which zirconium and aluminum salts are mixed together in an aqueous solution, subjected to heating to form the desired aluminum polymer distribution, and then rapidly dried to capture the polymer distribution achieved and to produce a dry, stable zirconium-aluminum salt. This process is directed to optimizing aluminum chemistry by shifting the aluminum polymer distribution in the final zirconium-aluminum salt toward smaller molecular weight, more effective, aluminum polymers.
Another similar method for making zirconium-aluminum salts is described in EP653203 (Rosenberg et al.) which teaches a process of making zirconium-aluminum salts by forming an aqueous mixture of a zirconium salt and glycine at ambient temperatures, combining the aqueous mixture with an aluminum chlorohydrate starting material, and rapidly drying the resulting aqueous mixture to form a zirconium-aluminum glycine complex. Rosenberg et al. teaches that an aqueous mixture of zirconium and aluminum salts is essential to forming the desired zirconium-aluminum glycine complex, but that the residence time for the zirconium and aluminum while together in solution should be minimized.
It is therefore generally taught in the antiperspirant art that zirconium-aluminum salts can only be formed by interacting various aluminum and zirconium materials together in an aqueous mixture. These aqueous mixtures, however, are not particularly stable during processing or formulation in that the aluminum and zirconium polymer distribution tends to shift when subjected to heat or if allowed to set or age for even a short period of time. To stabilize the polymer distribution, these aqueous mixtures are dried or otherwise dehydrated to form a more stable material that is substantially free of unbound water.
It has now been found that zirconium-aluminum salts can be made without relying upon as a process intermediate an aqueous solution containing a zirconium salt and an aluminum salt. Contrary to the historical teaching in the antiperspirant art, it has now been found that aluminum salts can be mixed with zirconium salts to form a zirconium-aluminum salt for use as an antiperspirant active, without involving any intermediate process step which combines the zirconium salt and the aluminum salt together in an aqueous solution. It has been found that the anhydrous process itself can result in the same zirconium-aluminum polymer distributions that were once believed to be made only from the reaction of zirconium and aluminum salts together in an aqueous medium.
It is therefore an object of the present invention to provide a new process for making zirconium-aluminum salts for use as antiperspirant active, without reliance upon the prior art methods which teach the use of aqueous solutions containing zirconium and aluminum materials together. It is a further object of the present invention to provide such a process by anhydrous mixing of aluminum salts and zirconium salts together to form the zirconium-aluminum polymer described in the art, wherein the anhydrous process never involves any aqueous mixture containing both aluminum and zirconium salts.